The principal object of this invention is to reduce the cost of manufacturing books and related products and at the same time produce an equal or stronger book or product. Important factors in the binding of such books are to improve methods of adhering sheets; to simplify production; and to reduce the number of operations necessary and the amount of highly skilled help.
We have discovered that equally strong, or stronger, binding can be done by holding the paper leaves together and subjecting them to ultrasonic vibration over areas of the leaves that are to be secured to one another.
In order to weld paper, which is a cellulosic product, it is necessary that the paper include, as one of its ingredients, a material such as a plastic, which will fuse at a temperature lower than the charring temperature of the cellulosic portion of the paper. The way in which the pressure is applied, or is necessary, depends upon whether the leaves are stationary during the welding operation or whether they are travelling continuously and with relative movement with respect to the welding station.
Another consideration is whether the connection is made along a line on which the paper is to be folded, as when welding a signature, or whether the weld is made along the spine portion of the leaves.
In either case, the vibration is produced by electrically-operated apparatus, which is conventional, and the energy is applied through an energy director, commonly referred to as a "horn," which localizes the vibrations so that they are confined to the portion of the paper which is to be connected together. If the paper has no movement with respect to the horn during the welding operation, the pressure can be applied by the horn against one side of the stack of leaves, and the other side of the stack can rest on an anvil, which can be provided with a depression if folded leaves are to be welded. A depression facilitates folding after welding.
When the paper is moving and being welded, the space between the horn and anvil (gap) must be set reasonably accurately. When properly set, the anvil need not be rotary, but can be stationary. When the proper gap is set and the ultrasonic means are in operation, a conveyor transports the paper to the horn and anvil for welding. If the ultrasonic means is not in operation, the paper will not pass between the horn and anvil when the gap is adjusted for normal operation.
Other objects, features and advantages of the invention will appear or be pointed out as the description proceeds.